Endotoxin-stimulated macrophages decrease bile acid uptake in WIF-B cells, a rat hepatoma hybrid cell line

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Abstract
Endotoxemia leads to cytokine-mediated alterations of the hepatocellular sodium-taurocholate-cotransporting polypeptide (ntcp). We hypothesized that stimulated macrophages are essential transducers for down-regulating hepatocellular bile salt uptake in response to endotoxin (lipopolysaccharide [LPS]) exposure. Using an in vitro model, we exposed mouse macrophages (IC-21 cell line) to LPS for 24 hours. Concentrations of cytokines tumor necrosis factor-α (TNF-α), interleukin (IL)-1β, and IL-6 increased 10.6-fold, 12.5-fold, and 444-fold, respectively, in LPS-conditioned IC-21 medium (CM) versus unconditioned IC-21 medium (UM). WIF-B rat hepatoma hybrid cells were incubated with either CM or UM or treated directly with medium containing recombinant TNF-α, IL-1β, and IL-6. [3H]Taurocholate ([3H]TC) uptake decreased in WIF-B cells exposed to either TNF-α (54% of control), IL-1β (78%), IL-6 (55%) as single additives, or in triple combination (TCC) (43%). A virtually identical decrease was observed after exposing WIF-B cells to CM (52%, P < .001). LPS had no direct effect on [3H]TC uptake. CM treatment did not decrease L-alanine transport in WIF-B cells. Blocking antibodies against TNF-α, IL-1β, and IL-6 restored the diminished [3H]TC uptake in cells exposed to TCC and CM to 87% and 107% of controls, respectively. Northern blotting revealed that ntcp messenger RNA (mRNA) expression was significantly reduced in WIF-B cells after exposure to CM, and in primary rat hepatocytes exposed to CM or TNF-α (68%, 14%, and 29% of control, respectively). We conclude that macrophages and their ability to secrete the cytokines TNF-α, IL-1β, and IL-6 may be essential in mediating the endotoxin-induced cholestatic effect of decreased hepatocellular bile salt uptake.